A Covid-19 modeller has challenged the Ministry of Health over its formal isolation guidance, arguing his own near two-week infection highlights the need for a smarter approach. Photo / Bevan Conley
A Covid-19 modeller has challenged the Ministry of Health over its formal isolation guidance, arguing his own near two-week infection highlights the need for a smarter approach. Photo / Bevan Conley
A Covid-19 modeller has challenged the Ministry of Health over its formal isolation guidance, arguing his own near two-week infection highlights the need for a smarter approach.
But the ministry says it has no plans to replace the current seven-day stay-at-home order with a "test-to-release" policy that Dr Dion O'Neale and fellow experts say could cut spread and allow many people to leave isolation earlier.
O'Neale and his partner and Covid-19 Modelling Aotearoa colleague Dr Emily Harvey caught the coronavirus earlier this month, following a trip to India.
"When I first tested positive, I didn't have any symptoms that would have kept me at home, which really showed the utility of rapid antigen tests in picking up infection early," he said.
In his case, it took 12 days of testing before he finally returned a negative result.
"Because I had a particularly long infection time, I probably would have saved others being infected by continuing to take isolation precautions beyond day seven," he said.
"But someone in my position could have said, right, I've done my seven days' isolation time, and gone back out into the community when they were clearly still infectious."
RATs remained an effective monitor of infectivity, he explained, in that they measured virus particles that weren't yet degraded.
"If your RAT is giving you any kind of line on that test strip, then it's found something that looks like a recently living virus – and that means it's not yet time to change your behaviour and assume you're no longer infectious."
We’ll, I’m pleased that that part of the infection is finished. Now just to get rid of the remaking symptoms. pic.twitter.com/oPwMTPl1TY
For these reasons, O'Neale had concerns with the ministry's current guidance, which advised people they could leave isolation seven days after either testing positive or developing symptoms, provided they were "not feeling unwell".
If they did still have symptoms, they were advised to stay home until 24 hours after symptoms resolved.
"In the past, they've had some information that's been just plain wrong – such as telling people you can keep testing positive on a RAT 28 days after infection," O'Neale said.
"If that's the case, then you've probably got an ongoing infection and you might be immune-suppressed, and should really be speaking with your physician."
Here, he suspected there'd been confusion with PCR testing, which included an amplification process that could indeed pick up fragments of virus well past the infectious period.
"We're still hearing stories about people who've phoned Healthline and been told, if it's been seven days, they're good to go, and not to worry about your RAT result."
While he said the ministry's advice had improved over time – and did acknowledge that RATs were useful and people should be cautious at the end of their infectious period – his own experience nonetheless highlighted the value of a test-to-release regime.
Modelling published in August, and led by Harvey, found that building a test-to-release requirement into our status quo – but with a maximum isolation period of 10 days - could cut the number of cases leaving isolation while still infectious by 40 per cent, with only minor increases in the average time spent in isolation.
Alternatively, they looked at a scenario where the minimum isolation period was only five days – with a maximum of 10 days – but where people were required to return two negative tests to leave.
This also led to a 40 per cent reduction in the number of infectious cases being released – but also a 20 per cent drop in the extra hours that people spent in isolation when no longer infectious.
"It's likely there'd be a lot of people who had the opposite experience to me, and perhaps could have left isolation sooner," O'Neale said.
In any case, he felt it crucial that the Government kept some isolation requirement for infected people - something Australia scrapped earlier this month – among our few remaining virus-fighting controls.
The ministry told the Herald that, with an upward trend in cases and growing concern about new Omicron subvariants, the seven-day isolation period remained an "important core measure".
Covid-19 modeller Dr Dion O'Neale. Photo / Supplied
While it was regularly assessing measures – the next review is scheduled for late November – it had no plans to bring in a RAT-based test-to-release policy.
"The ministry does not advise cases undertake additional RATs after their initial positive test," a spokesperson said.
"A positive RAT test does not always indicate that a person is infectious and it is infectiousness that is important when considering the effectiveness of isolation requirements.
"Infectiousness reaches a peak shortly after symptom onset, and RATs become positive usually within 48 hours of symptom onset.
"Therefore, RATs first become effective just as infectiousness is peaking or while it is already decreasing and subsequent positive test results become progressively less indicative of infectiousness."
They said the seven-day isolation period for several reasons: one being that ensured people stayed home over their "most infectious period", and another that a large proportion of people diagnosed were unwell for that week and often unable to work.
"Thirdly this policy is simple and easy to implement, an important factor in ensuring high levels of public compliance with a public health measure that requires significant disruption to their lives," they said.
"We continue to monitor and evaluate data to inform our future approach to testing and isolation."
Yet O'Neale said that the evidence was clear that multiple international, peer-reviewed, scientific studies have shown that the results of rapid antigen tests tracked closely with infectivity.
"After an initial positive test, there is a small lag of around 24 hours between no longer being able to grow living virus from a sample and testing negative on an antigen test," he said.
"RATs are even able to illustrate the effect of decreasing infectivity in the later stages of an infection through the decrease in darkness of a test strip."
O'Neale said it was "disappointing, to say the least" that the ministry was continuing to advise people not to use RATs after an initial positive test.
Harvey was similarly frustrated about the guidance, noting former director general of health Dr Ashley Bloomfield's advice that people should act as if though infectious and take precautions up until day 10.
"Keeping the legally required isolation period at a flat seven days is an understandably simpler policy to communicate to the public and to enact through legislation," she said.
"But what I don't understand is why the ministry have not used the best evidence and data in their recommendations and advice."
Otago University epidemiologist Dr Amanda Kvalsvig considered the guidance a "disappointing approach to public health communication".
"RAT technology provides a quick check for New Zealanders who want to know whether it's safe to return to work or attend a family gathering after an infection," she said.
"Not everyone will make use of the opportunity, but everyone should have access to sensible, evidence-informed guidelines about how best to use the tests to protect others."
